WO2010127598A1 - Combined method for high energy ray probing and locating - Google Patents

Abstract

A method for high energy ray probing and locating is provided. First, scintillation crystals for capturing high energy ray are arranged into a regular array; a plurality of photomultiplier tubes (PMTs) of different sizes are assembled into combined arrangements so that PMTs of smaller sizes are located in the center of PMTs of larger sizes; the scintillation crystals array is bonded with a composite PMT array with optical cement, obtaining combined detectors for high energy ray; scintillation lights are generated when high energy gamma rays are incident upon the scintillation crystals array of the above combined detectors for high energy ray, electric pulse signals are obtained after the scintillation lights are multiplied by the composite PMT array, and then the electric pulse signals are processed to obtain information like, a coordinate of high energy ray in the scintillation crystal array, energy and time. The method of present invention provides high energy ray detection with higher efficiency and more uniformity, and the method has higher spatial resolution, higher energy resolution and, in the mean time, quick responses.

Description

 Method for detecting and locating high-energy ray in the technical field

 The invention relates to a method for detecting and locating high energy rays, and belongs to the technical field of radiation detection imaging. Background technique

 High-energy ray detection technology usually uses a scintillation crystal that can effectively block radiation rays and absorb its energy to emit light as a detection material, and then photoelectrically convert and amplify the weak optical signal with a high-gain photoelectric multiplying device to generate an electrical pulse signal. By collecting these pulse signals to obtain information on the energy, time and spatial position of high-energy rays, such solid-state detectors are commonly referred to as scintillation detectors.

 When high-energy rays are incident inside the scintillation crystal, depending on the amount of energy, different proportions of photoelectric effect, Compton scattering effect and electron pair effect are usually generated. The energy of the ray itself is finally absorbed by the scintillation crystal, and the emission is extremely weak. Flashing light. For the scintillation light in the visible or ultraviolet region, after photoelectric conversion, the high-sensitivity signal amplifier (such as photomultiplier tube) is used to detect all the information of the high-energy ray, such as the pulse signal intensity of the photomultiplier output. The energy of the high-energy ray; the time at which the pulse signal occurs reflects the incident time of the high-energy ray; the intensity distribution of the pulse signal in the plurality of photomultiplier tubes reflects the incident position of the high-energy ray and the like. Traditional scintillation detectors are characterized by high detection efficiency, high signal-to-noise ratio and fast response time. They are widely used in nuclear medicine, article safety inspection, high-energy physics and cosmic ray detection. The main means of lacking.

 The structure of the conventional scintillation detector is relatively simple. Especially when performing the detection and positioning, a plurality of the same photomultiplier tubes are usually used to couple the scintillation crystal array to determine the position of the incident position of the high-energy ray, and the gap between the photomultiplier tubes is different. A large area of detection blind spots, so that the detection efficiency of the entire detector imaging is uneven and its spatial resolution is relatively low, so how to improve detection efficiency, imaging uniformity and spatial resolution is the research focus of radiation detection imaging technology.

1 is the basic structure of a conventional scintillation detector. The basic structure of such a detector is generally composed of a scintillation crystal array module coupled to four photomultiplier tubes (PMTs) of the same size and shape. Figure 2 is a top plan view of the conventional scintillation detector showing the scintillation crystal array module covering the surface of the detection window of the four photomultiplier tubes. The scintillation crystal array is usually formed by bonding a sliver type of scintillation crystal material and a reflective film. Between the scintillation crystal array module and the photomultiplier glass window, it can be directly bonded or placed by high transparency optical glue Photoconductive materials (including organic plastics, glass, optical fibers, etc.) are indirectly coupled between the scintillation crystal and the photomultiplier tube.

When high-energy rays are incident on the scintillation crystal array, each high-energy ray excites a single scintillation single crystal at its incident position, and the scintillation light is emitted in a single crystal by photoelectric effect or Compton scattering effect, according to different scintillation crystal material characteristics. The number of corresponding scintillation photons is usually on the order of 10 ³ - 10 ⁴ , and the wavelength is generally between 200 nm and 600 nm.

(UV or visible range). Due to the reflection of the single crystal surface reflective material, the scintillation light will be trapped in the single crystal body and reflected multiple times and sequentially propagated from the front end of the crystal to the photomultiplier tube at the rear end. When encountering the crystal surface of the non-reflective material, the scintillation light is transmitted into its adjacent scintillation crystal unit and continues to propagate. Finally, the pulse signal is collected and generated by the incident glass port of the photomultiplier tube, so the intensity of the pulse signal at each photomultiplier tube The distribution reflects the incident position of the high-energy ray. The sum of the intensity of the pulse signal is proportional to the incident energy of the high-energy ray. The generation time of the pulse signal is related to the occurrence time of the incident ray. The spatial positioning accuracy of the detector is caused by a single flicker. The cross-sectional size of the crystal is determined.

For a conventional scintillation detector, the ratio of the four photomultiplier tubes to different intensity pulse output signals generated by the same incident high-energy ray excitation can be used to estimate the position of the incident ray in the scintillation crystal array. For the Anger logic positioning method. If the four photomultiplier tubes produce voltage signal strengths of V _A , V _B , V, respectively. , V _D , then the spatial position X, Y and energy E of the high energy ray are:

 V + V

 ~ V +v +v +v

Y v ' +v

 V + v + v + v

E = + V _n + V + V _n

Summary of the invention

 The object of the present invention is to propose a method for detecting and locating a composite high-energy ray by performing signal acquisition of a scintillation detector by using an optimized combination of photomultiplier tubes of different sizes or shapes, and accomplishing high energy by bonding a scintillation crystal array with a photo-adhesive bond. The functions of detecting, amplifying, locating, and imaging the ray, and simultaneously acquiring the time, space, and energy information of the high-energy ray acting on the scintillation crystal array.

The method for high energy ray detection and positioning proposed by the invention comprises the following steps - (1) arranging scintillation crystals for capturing high energy rays into a square array;

 (2) assembling a plurality of photomultiplier tubes of different sizes into a composite arrangement, so that the smaller size photomultiplier tube is at the center of the larger size photomultiplier tube;

 (3) directly bonding the above-mentioned scintillation crystal array and the composite photomultiplier tube array with optical glue, or bonding the photoconductive material between the above-mentioned scintillation crystal array and the composite photomultiplier tube array with optical glue, Obtaining a composite high energy ray detector;

 (4) When high-energy gamma rays are incident on the scintillation crystal array of the above composite high-energy ray detector, scintillation light is generated, and an electric pulse signal is obtained by amplification by the composite photomultiplier tube array, and the electric pulse signal is amplified and decoded. The coordinates of the high energy ray in the above scintillation crystal array are obtained by the weight distribution of the pulse signal in the photomultiplier tube array.

 In the above method, the material of the scintillation crystal is bismuth ruthenate, strontium silicate, strontium silicate, strontium silicate, strontium fluoride, sodium iodide, cesium iodide, lead tungstate or strontium aluminate. .

 In the above method, the photoconductive material is any one of organic plastic, glass or optical fiber.

In the above method, the method for decoding the electrical pulse signal is: providing N photomultiplier tubes, the generated voltage signal strengths are V, V ₂ , V ₃ ～ V _N , respectively, and the high energy ray is in the scintillation crystal array. The coordinates of the position coordinate X direction are: the sum of the pulse electrical signals of all the photomultiplier tubes in the X direction divided by the sum of the pulse electrical signals of all the photomultiplier tubes; the coordinates of the x direction are: the pulse electric power of the photomultiplier tubes in all the x direction The sum of the signals is divided by the sum of the pulsed electrical signals of all photomultiplier tubes; the energy of the high energy rays is: the sum of the pulsed electrical signals of all photomultiplier tubes.

 The method for high energy ray detection and positioning proposed by the invention has the following features and advantages:

 1. More efficient and more uniform high-energy ray detection: Due to the different size or shape of the photomultiplier tube combination, the detection blind zone between the photomultiplier tubes can be effectively reduced, and the densely-distributed tube of the photomultiplier tube is increased, thereby increasing The detection efficiency and detection uniformity of the flickering light emitted in the scintillation crystal make the imaging quality of the high-energy ray detection higher.

2. Higher spatial resolution: Since the method uses a highly dense photomultiplier tube to collect all the scintillation crystal luminescence, it can increase the detectable effective scintillation light yield, thereby reducing the statistical noise of the pulse signal, The imaging resolution of the detection is increased. The luminescence yield of different scintillation crystal materials is different. If the LS0 or LYS0 crystals with high yield are used to form the detection array, the composite ray detection method will be better than the traditional scintillation detector resolution in the commercial market. 3, higher energy resolution: Because the method uses high-density photomultiplier tube to effectively collect all the scintillation crystal luminescence, it can effectively detect more flickering light and reduce the statistical noise of the signal, thus making the detection The energy resolution is also improved.

 4. Independent judgment without dry winding: For high-resolution composite high-energy ray detectors, since the scintillation crystal modules are optically isolated, the scintillation light can only propagate in the single crystal array module it generates, so multiple crystal array modules The signal between them is not concatenated.

 5. Fast response: Due to the small size of the photomultiplier tube in the center, the photomultiplier tube with faster response time can be selected as the trigger time, and the signal is greatly reduced in the transit time of the photomultiplier tube, making this composite The detection method responds more quickly to incident high-energy rays and has the potential for time-of-flight measurement techniques (T0F).

 6. Compact structure: Compared with the traditional high-energy ray detector, the integration of the detector is more compact and greatly reduced due to the addition of the composite photomultiplier tube without changing the overall detector dimensions. The dead zone area of the detector.

 In summary, the outstanding advantages of the hybrid high-energy ray detector are not only the improvement of space, energy resolution and uniform imaging, but also the cost can be lower than the traditional scintillation detector. DRAWINGS

 Figure 1 is a schematic diagram of the principle of a conventional scintillation detector.

 Figure 2 is a plan view of Figure 1.

 Figure 3 is a schematic illustration of the principle of a scintillation detector constructed by the method of the present invention.

 Figure 4 is a plan view of Figure 3.

 Figure 5 is a block diagram of the signal processing of the method of the present invention.

 Figure 6 is a schematic illustration of an 8 X 8 lattice consisting of bismuth ruthenate (BG0) crystals in one embodiment of the process of the present invention. Figure 7 is a high energy ray spectrum of cerium (Cs-137) obtained by an embodiment of the method of the present invention.

 Figure 8 is a photograph of the detection of high energy rays by the method of the present invention.

 In Fig. 1 - Fig. 4, 1 is a scintillation crystal array, and 2 is a photomultiplier tube (hereinafter referred to as PMT). detailed description

 The method for high energy ray detection and positioning proposed by the invention comprises the following steps:

(1) arranging scintillation crystals for capturing high energy rays into a square array; (2) assembling a plurality of photomultiplier tubes of different sizes into a composite arrangement, so that a photomultiplier tube having a smaller size is placed at the center of the larger size photomultiplier tube;

 (3) directly bonding the scintillation crystal array and the composite photomultiplier array directly to each other with an optical glue, or bonding the photoconductive material between the scintillation crystal array and the composite photomultiplier tube array with an optical glue, Obtaining a composite high energy ray detector;

 (4) When high-energy gamma rays are incident on the scintillation crystal array of the above composite high-energy ray detector, scintillation light is generated, and an electric pulse signal is obtained after being amplified by the composite photomultiplier array, and the electric pulse signal is amplified and decoded. The coordinates of the high energy ray in the above scintillation crystal array are obtained by the weight distribution of the pulse signal in the photomultiplier tube array.

 Schematic diagram of a scintillation detector constructed using the method of the present invention. As shown in Figure 3, it consists of two sets of circular photomultiplier tubes of different sizes, of which PMT1, PMT2, PMT3, PMT4 are the same size and equal to twice the diameter of PMT5, and PMT5 is embedded as four small-sized photomultiplier tubes. The center of the large-size photomultiplier tube detects the blind zone. Therefore, increasing the photomultiplier tube (PMT5) of this center can effectively compensate for the omission of the scintillation light in the central detection blind zone, and greatly improve the uniformity of high-energy ray detection.

4 is a top view of FIG. 3 in which a scintillation crystal array module is optically coupled to a front end window of five photomultiplier tube arrays. For the scintillation event of the excitation of the same high-energy ray, the signal generation time of the central photomultiplier tube (PMT5) can characterize the incident time of the high-energy ray, and the sum of the intensity of the pulse signals of all the five photomultipliers is proportional to the incident intensity of the high-energy ray. The modified Anger logic positioning method can obtain the incident position of high energy rays. If the voltage signal intensities generated by the five photomultiplier tubes are Vi, V ₂ , V ₃ , V ₄ , V ₅ , respectively, the spatial positions X, Y and energy E of the high energy rays are:

_ _ V ₂ +V ₄ + *V ₅

_γ _ ν, +ν ₂ + *ν ₅

~ ν _λ +ν ₂ +ν^+ν+ν,

E = V, +V ₂ +V ₃ +V ₄ +V ₅

 α is a weighting factor and ranges from 0 to 1.

In the method of the present invention, the scintillation crystal material used may be bismuth ruthenate (BG0), strontium silicate (LS0), strontium silicate (LYS0), strontium silicate (GS0), barium fluoride (BaF ₂ ), iodine. Any of sodium (Nal), cesium iodide (Csl), lead tungstate (PbW0 ₄ ) or yttrium aluminate (YaP). Figure 5 is a block diagram showing the signal processing flow of the method of the present invention. The scintillation light excited by the same incident high-energy ray will cause each photomultiplier tube to generate an electric pulse. After each pulse signal is preamplified and amplified, the summation circuit is added to generate a voltage pulse reflecting the ray energy. Similarly, the normalized position information X and Y are obtained by the addition and division of the partial photomultiplier tube electrical pulse signals, and the pulse signal of the central photomultiplier tube produces the incident time information. The following is an embodiment of the method of the invention:

 Experimental condition

 Scintillation crystal material: bismuth citrate (BG0)

 Scintillation crystal structure: 8 rows and 8 columns composed of 8 X 8 strontium strontium crystal lattice. As shown in Figure 6, the single crystal has a cross-section of 9. 0 X 9. 0mm and a length of 20

 Gamma ray source: 铯 (Cs-137) point source, intensity 100μ (^, energy 662KeV

 Photomultiplier tube: 4 Photonis XP2040 (diameter 39 mm)

 1 Photonis XP1912 (diameter 19 mm)

 Number of photomultiplier tubes: 5

Photomultiplier tube gain: ~1 X 10 ⁶

Photomultiplier tube cathode voltage: - _1100V

 Photomultiplier tube anode voltage: 0V (ground) Analysis of experimental results:

 As shown in Fig. 6, the scintillation crystal of the composite high-energy ray detector is composed of 8 rows and 8 columns of bismuth citrate crystals, and the 铯(Cs-137) gamma ray point source is 30 cm away from the detector. The ray is incident on the 8×8 strontium strontium crystal lattice in parallel, and the scintillation light excited by the ray is amplified by the 5 photomultiplier tubes of the composite structure and then calculated by the Anger logic positioning circuit board to obtain the energy of the gamma ray. , time and space positioning information.

 Figure 7 is the energy spectrum of the 铯(Cs-137) high-energy ray obtained by the composite high-energy ray detector measured by the channel analyzer. The value of the horizontal axis is proportional to the energy of the gamma ray, and the vertical axis corresponds to the energy position. Counting rate, where the maximum peak corresponds to the characteristic energy of the gamma ray emitted by Cs-137 (662KeV), and the energy resolution of the microchannel plate type scintillation detector is 21%

Fig. 8 is a view showing the detection of high-energy rays by the composite high-energy ray detecting method of the present invention, that is, the spatial distribution of the incident position of the high-energy ray, wherein the 8×8 lattice structure is clearly visible. The gray level of the image represents the count rate, the darker the color Where the higher the intensity of gamma rays, a single cross-sectional dimension of the BGO crystal composite high energy radiation detectors is 9mm, the total gamma ray count of 10 ^5.

Claims

Claim A method for high energy ray detection and positioning, characterized in that the method comprises the following steps:  (1) arranging scintillation crystals for capturing high energy rays into a square array;  (2) assembling a plurality of photomultiplier tubes of different sizes into a composite arrangement, so that the smaller size photomultiplier tube is at the center of the larger size photomultiplier tube;  (3) directly bonding the scintillation crystal array and the composite photomultiplier array directly to each other with an optical glue, or bonding the photoconductive material between the scintillation crystal array and the composite photomultiplier tube array with an optical glue, Obtaining a composite high energy ray detector;  (4) When high-energy gamma rays are incident on the scintillation crystal array of the above composite high-energy ray detector, scintillation light is generated, and an electric pulse signal is obtained after being amplified by the composite photomultiplier array, and the electric pulse signal is amplified and decoded. The coordinates of the high energy ray in the above scintillation crystal array are obtained by the weight distribution of the pulse signal in the photomultiplier tube array.  2. The method according to claim 1, wherein the material of the scintillation crystal is barium strontium silicate, barium silicate, barium silicate, barium silicate, barium fluoride, sodium iodide, iodide Any of bismuth, lead tungstate or strontium aluminate.  3. The method of claim 1 wherein said photoconductive material is any one of an organic plastic, glass or optical fiber. 4. The method of claim 1 wherein the method of decoding the electrical pulse signal of the high energy ray detector consisting of a crystal array and five different size photomultiplier tubes is: if four photomultiplier tubes are surrounding The resulting voltage signal strengths are Vi, V ₂ , V ₃ , V ₄ and the voltage signal strength generated by the central photomultiplier tube V ₅ , then the spatial position X, Y and energy E of the high energy ray are: Χ_ V ₂ +V ₄ +a*V ₅ ~ ν,+ν ₂ +ν ₃ +ν ₄ + ν ₅ ~v^+v v+v +v Ε= + + Where α is a weighting factor and ranges from 0 to 1. For the scintillation luminescence of the excitation of the same high-energy ray, the signal generation time of the central photomultiplier tube can characterize the incident time of the high-energy ray, and the sum of the intensity of the pulse signals of all the five photomultipliers is proportional to the incident intensity of the high-energy ray. 5. The method according to claim 1, wherein the method for decoding the electrical pulse signal is: providing a photomultiplier tube, the generated voltage signal strengths are respectively V ₂ , H, then the high energy The coordinates of the position coordinate X direction of the ray in the scintillation crystal array are: the sum of the pulse electrical signals of all the X-direction photomultiplier tubes divided by the sum of the pulse electrical signals of all the photomultiplier tubes; the coordinates of the Y direction are: All Y directions The sum of the pulse electrical signals of the photomultiplier tube is divided by the sum of the pulse electrical signals of all photomultiplier tubes; the energy of the high energy ray is the sum of the pulse electrical signals of all photomultiplier tubes.